Continuity at radio coax connection

Discussion in 'CB Radio Forum' started by Windmill Hill, Jul 8, 2019.

  1. Windmill Hill

    Windmill Hill Bobtail Member

    25
    7
    May 26, 2019
    Central Indiana
    0
    Well, I thought all was good when I ended my last thread:
    Cobra 29LX and Astatic Road Devil problem
    However, I started having problems with the coax shorting out again or grounding issues "antenna warnings". So, I've started all over. I purchased a President McKinley radio and repositioned my Wilson 2000 to the center of the truck (Ford Ranger, not my Mack). Now this is on a fiberglass topper with a new gumdrop mount, but I put a plate of metal under the fiberglass and bonded everything...plate to truck bed to cab and then to the frame and used my ohmmeter to verify proper ground. I also ran my positive from the radio directly to the battery with an inline fuse and grounded the radio chassis as well. So I know that it is well grounded. I've tuned the antenna with initial results of 1.1:1 on ch1 and 1.2:1 on ch40 but it will not stay consistent and I can't receive anyone most of the time and SWR reaching into the high 2's and has spiked upwards to 4 using both the internal and external meters. This all started as you know when I first keyed up that power mic I thought I just had to have on the Cobra 29LX. So I'm thinking it may have fried the antenna or at least caused a short in it considering the fluctuation in readings and it's really the only component I haven't changed. I have ordered another coax (Belden w/Anthenol connectors) and I will also put a new power supply on it. Antenna is next in line...or actually should have been first, opinions? Oh, and just out of curiosity, is this normal (Cobra 29LX not the President) ⬇️
    20190630_010802.jpg
     
  2. rabbiporkchop

    rabbiporkchop Road Train Member

    8,872
    5,633
    Feb 9, 2012
    Wapwallopen, Pa
    0
    Not sure what you're measuring in the picture. If you had a magnet Mount antenna that was known to be good it would make troubleshooting the radio much easier.
     
    Windmill Hill Thanks this.
  3. Ridgeline

    Ridgeline Road Train Member

    14,357
    52,750
    Dec 18, 2011
    Michigan
    0
    Ok a few thoughts ...

    First what you see on the radio is normal, there is a tuning and detection system that shows resistance.

    Second is if you are getting fluctuation, the there are only a couple places this happens, the coax if it is shorted or pinched and the vehicle is moving and the other is the antenna ground system, which I am thinking is the problem. A third possilbity is the radio has an issue with the rf ground.
     
    Windmill Hill Thanks this.
  4. Powder Joints

    Powder Joints Subjective Prognosticator

    5,402
    3,790
    Sep 25, 2007
    Rosamond, SoCal
    0
    Test leads are backwards.But do not understand what it is you think your measuring....Key up the radio see if the meter smokes then you know it was transmitting
     
    Windmill Hill Thanks this.
  5. Windmill Hill

    Windmill Hill Bobtail Member

    25
    7
    May 26, 2019
    Central Indiana
    0
    I was measuring to see if there was continuity from the center post to the outside of the connector. I knew that there shouldn't be any at those coax points, so I just figured the same for the radio side. Yeah, the leads are backwards but I was measuring ohms...didn't realize that made a difference with the continuity. Still learning and I'm glad that the reading is normal and very grateful for this forum and all the help and patience from such a great group of people
     
  6. Powder Joints

    Powder Joints Subjective Prognosticator

    5,402
    3,790
    Sep 25, 2007
    Rosamond, SoCal
    0
    Theres going to be something there since your looking into the finals and chokes backwards, not sure what you should actually see, some resistance.
    for checking continuity polarity dies not matter. Good Luck
     
    Windmill Hill Thanks this.
  7. craig_sez

    craig_sez Road Train Member

    3,933
    1,926
    Sep 5, 2013
    novascotia,Canada
    0
    Get rid of that gumdrop ant stud bs..Those are garbage...Grab a wilson hd alumium looking stud...
     
    Windmill Hill Thanks this.
  8. handlebar

    handlebar Heavy Load Member

    My feeling is that what the DMM is showing is that the battery polarity diode is not (yet) blown into a short. The Vcc (or A+, if you wish) is fed to the collector of the final amp transistor. That big Silicon diode is reverse biased, so it's indicating the junction as intact. If the meter showed ~0v, it would mean either that the protection diode has shorted, or the tech has reversed the polarity with the leads.
    So whilst,this my not solve any problems now, it's nice to see the protection stage is still present and doing its job.

    Diddly dahdidah
     
    Last edited: Jul 12, 2019 at 12:49 PM
    Reason for edit: Typo
    Powder Joints and Windmill Hill Thank this.
  9. Windmill Hill

    Windmill Hill Bobtail Member

    25
    7
    May 26, 2019
    Central Indiana
    0
    Thank you for that explanation. Good to know all (or most) is good with that particular radio. It's been a great cb and have always had good reports on sound and clarity.
     
  10. Ridgeline

    Ridgeline Road Train Member

    14,357
    52,750
    Dec 18, 2011
    Michigan
    0
    Not really, there is a blocking cap between the collector and the tuning circuit. the resistance he is seeing is part of the tuning circuit there is a resistor going to ground before the swr circuit.
     
    Windmill Hill Thanks this.
  • Draft saved Draft deleted